The present invention relates to a DC motor servo system utilizing an application specific integrated circuit (ASIC) under the influence of a microcomputer for controlling a DC motor.
In many systems a DC motor is employed as a prime mover. One such system is a novel mail processing system. The mail processing system employs a plurality of system modules for processing envelopes. Particularly, the mail processing system includes a feeder section having a envelope stack receiving module, a singulation module, and an envelope flap moistening module. The feeder section is followed by a mailing machine section having an integral scale module, tape module, meter module and transport module.. A more detailed description of the mail processing system is presented in U.S. Pat. No. 4,935,078, entitled "High Through-Put Mail Processing System".
The mail processing system of particular interest offers the advantage of providing a minimum foot print and high through-put rate. In order to achieve this advantage, realizing that the mail processing system must accommodate a variety of different sized envelopes, it is necessary for the microcomputer system to exercise exacting servo control over the motors associated with one or more of the modules. In order to achieve the high through-put rate in light of the minimum feed path (foot print), a system constraint is to accommodate maximum acceleration and deceleration of a respective motor under system loads without destructively over-driving the motor.
It has been considered advantageous to provide the mail processing system with not only a minimum feed path but also minimum overall profile. In order to obtain this advantage along with the accompanying cost advantage, motors have been selected which provide the necessary transport torque, as a result, the smallest motor which provides sufficient transport torque has been chosen. In order to achieve the necessary accelerations, the motor must be overdriven for a short period. It has been empirically determined that the motors can survive the accelerator phase provided the motor is closely servo-ed by the motor controller. However, a particularly destructive condition occurs during an envelope jam. An envelope jam can cause a motor stall condition. This condition can be destructive to the motor as the motor controller is causing the motor to be overdriven, i.e., the motor controller is causing the motor driver to deliver excessive current or voltage to the motor for a prolonged time due to the stall condition.